Mask assembly



FIG. 1 is a front perspective view of a mask assembly according to our new design;

FIG. 2 is a side view of the mask assembly thereof; and,

FIG. 3 is a front view of the mask assembly thereof.

This design is directed to a mask assembly. Where included, broken lines illustrate environmental structure of the mask assembly, which forms no part of the claimed design. 

The ornamental design for a mask assembly, as shown and described. 